The present application claims priority to Japanese Patent Application No. 2000-078675, filed Mar. 21, 2000, entitled xe2x80x9cMethod for Measuring Internal Stress of Reticle Membrane and Device Therefor, and Method for Manufacturing Semiconductor Devicexe2x80x9d. The contents of that application are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to an apparatus and method for measuring the internal stress of a membrane formed in a reticle. Further, the present invention relates to a method for manufacturing a semiconductor.
2. Discussion of the Background
As semiconductors are becoming more highly integrated, integrated circuits are required to be further detailed and miniaturized. At the same time, in order to print a more detailed and smaller pattern, an exposure device capable of printing at a higher resolution is needed. In response to such demand, an exposure device utilizing a charged particle beam such as an electron beam has been attracting attention.
Among various charged particle beam exposure devices, an exposure device which utilizes a multi-segment exposure transfer method has good throughput and is becoming a mainstream. In this type of exposure devices, a pattern to be formed on one chip is segmented into small transfer regions called xe2x80x9csub-fieldsxe2x80x9d which are usually about 250 xcexcmxc3x97250 xcexcm each on a wafer. Each sub-field is exposed respectively, and thus the pattern for the one chip is formed on a wafer in its entirety by stitching all the sub-fields on the wafer.
A reticle for the multi-segment exposure method has a number of thin membranes supported by strut portions. For example, when a pattern is transferred by reducing its size to xc2xc, struts support each membrane having approximately 1 mmxc3x971 mm. Further, in a reticle called a xe2x80x9cstencil typexe2x80x9d, an aperture corresponding to a pattern is formed in its membranes, using the lithography process. When a sub-field is irradiated by a charged particle beam, some charged particles pass through the aperture and form their images on a wafer while the other charged particles are either absorbed or scattered by the membrane and leave no effect on the wafer. Thus, the pattern corresponding the aperture in the reticle is exposed and transferred onto the wafer.
In forming an aperture corresponding to a pattern in a reticle, the internal stress of its membranes must be considered. If a large internal stress remains in a membrane, an aperture may be deformed due to the internal stress as the aperture is being formed. As a result, the aperture does not have an intended shape.
Consequently, before processing a reticle for apertures, the internal stresses of its membranes are measured, and only reticles with the membranes whose internal stresses are within a permissible range are selected for use.
The internal stresses of the membranes is measured by generating a sound having a certain frequency by a piezoelectric element, oscillating each membrane by the sound, detecting the amplitude of the vibration, finding out a resonance frequency of the membrane, and calculating the internal stress of the membrane based on the resonance frequency thus found. The amplitude of the vibration is detected by using a light lever formed by a multi-segment photo detector and a laser such as a semiconductor laser.
However, to calculate the internal stress of a membrane based on a resonance frequency found in the manner described above, it is necessary to know beforehand what Young""s modulus of the membrane is. Hence, by using some other methods or processes, it is necessary to measure Young""s modulus of the membrane in advance. For example, the Bulge method and the vibration lead method have been used to measure Young""s modulus of a membrane. In the Bulge method, a membrane is pressurized without moving it, and bulging of the membrane is measured. In the vibration lead method, a resonance frequency is measured by preparing a cantilever. As a consequence, a measurement of the internal stress of a membrane requires to use a number of measuring devices and prepare a number of data. The conventional methods for measuring the internal stress of a membrane therefore result in onerous and time consuming processes.
According to one aspect of the present invention, an apparatus for measuring internal stress of a membrane formed in a reticle includes a temperature adjustment device, a resonance frequency finding device and a stress calculating device. The temperature adjustment device is configured to change a temperature of the membrane from a first temperature to a second temperature. The resonance frequency finding device is configured to find a first resonance frequency of the membrane at the first temperature and a second resonance frequency of the membrane at the second temperature. The stress calculating device is configured to calculate the internal stress based on the first and second resonance frequencies.
According to another aspect of the present invention, a method for manufacturing a semiconductor includes changing a temperature of the membrane formed in a reticle among a plurality of reticles from a first temperature to a second temperature. A first resonance frequency of the membrane at the first temperature and a second resonance frequency of the membrane at the second temperature are found. The internal stress is calculated based on the first and second resonance frequencies. A reticle in which the internal stress of the membrane is within a predetermined range is selected among the plurality of reticles. A pattern is formed on the selected reticle. The pattern formed on the reticle is transferred onto a wafer.
According to yet another aspect of the present invention, a computer readable media for controlling a computer to perform the steps of changing a temperature of the membrane from a first temperature to a second temperature; finding a first resonance frequency of the membrane at the first temperature and a second resonance frequency of the membrane at the second temperature; and calculating the internal stress based on the first and second resonance frequencies.